CHEM 1412 SAMPLE FINAL EXAM

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1 CHEM 1412 SAMPLE FINAL EXAM PART I - Multiple Choice (2 points each) 1. In which colligative property(ies) does the value decrease as more solute is added? A. boiling point B. freezing point and osmotic pressure C. osmotic pressure D. freezing point and vapor pressure 2. What is the molarity of a solution prepared by dissolving 25.2 g of Na 2 CO 3 in 600 ml of solution? A M B M C M D M 3. What is the freezing point of an aqueous glucose solution that has 25.0 g of glucose, C 6 H 12 O 6, per g of H 2 O? (K f for water = 1.86 C /m) A C B C C C D C 4. What is the osmotic pressure produced by a 1.20 M glucose (C 6 H 12 O 6 ) solution at 25 C? A atm B atm C atm D atm 5. The vapor pressure of pure ethanol at 60 C is 349 mm Hg. Calculate the vapor pressure at 60 C of a solution prepared by dissolving 10.0 mol of naphthalene in 90.0 mol of ethanol. A. 600 mm Hg B. 314 mm Hg C mm Hg D mm Hg 6. For first-order reactions, the rate constant, k, has the units A. M s 1 B. M 1 s 1 C. M 2 s 1 D. s 1 7. For second-order reactions the slope of a plot of 1/[A] versus time is A. k B. k/[a] 0 C. kt D. k 8. If the reaction 2A + 3D Products is first order in A and second order in D, then the rate law will have the form Rate = A. k[a] 2 [D] 3 B. k[a][d] C. k[a] 2 [D] 2 D. k[a][d] 2 9. In the first-order reaction A Products, the initial concentration of A is 1.56 M and the concentration is M after 48.0 min. What is the value of the rate constant, k? A X 10 2 min 1 B X 10 2 min 1 C X 10 2 min -1 D X 10 2 min 1

2 10. Consider the reaction 2 HI (g) H 2 (g) + I 2 (g). What is the value of the equilibrium constant, K c, if at equilibrium, [H 2 ] = 6.50 X 10 7 M, [I 2 ] = 1.06 X 10 5 M, and [HI] = 1.87 X 10 5 M? A X 10 7 B X 10 2 C X D In the mechanism below, which substance is the catalyst in the reaction? Step 1: C + ClO 2 ClO + CO Step 2: CO + ClO 2 CO 2 + ClO Step 3: ClO + O 2 ClO 2 + O Step 4: ClO + O ClO 2 A. ClO 2 B. CO 2 C. O D. CO 12. For the reaction CaO (s) + CO 2 (g) CaCO 3 (s) the equilibrium constant expression for K eq is A [CO 2 ] B. 1 / [CO 2 ] C. [CaO][CO 2 ] / [CaCO 3 ] D. [CaCO 3 ] / [CaO][CO 2 ] 13. The value of K p for the reaction 2 NO 2 (g) N 2 O 4 (g) is 1.52 at 319 K. What is the value of K p at this temperature for the reaction N 2 O 4 (g) 2 NO 2 (g)? A B C X 10 4 D Which of the following is true for the following voltaic cell? Zn (s) Zn 2+ (aq) Cr 3+ (aq) Cr (s) A. The electrons flow from cathode to the anode. B. The electrons flow from the zinc electrode to the chromium electrode. C. The electrons flow from the chromium electrode to the zinc electrode. D. Zinc is reduced in the reaction. 15. How many electrons are transferred in the following reaction? 2 ClO H I 5 I 2 + Cl H 2 O A. 10 B. 12 C. 5 D A voltaic cell has E cell = V. The cell reaction A. is not spontaneous B. has K = 1 C. has G = 0 D. has a negative G

3 17. Which energy conversion takes place in a galvanic cell? A. electrical to chemical B. chemical to electrical C. mechanical to chemical D. electrical to mechanical 18. The value of K c for the reaction C(s) + CO 2 (g) 2CO(g) is 1.6. What is the equilibrium concentration of CO if the equilibrium concentration of CO 2 is 0.50 M? A B C D Consider the following reaction: 2 SO 3 (g) 2 SO 2 (g) + O 2 (g) H = +198 kj All of the following changes will shift the equilibrium to the left ( ) except one. Which one will not cause the equilibrium to shift to the left? A. removing some SO 3 B. decreasing the temperature C. increasing the container volume D. adding some SO Calculate the ph of a solution which has [OH ] = M. A B C D Which conjugate base of the following Brønsted-Lowry acids is incorrect? (compound, conjugate base) A. HClO, ClO B. H 2 S, HS C. H 2 SO 4, HSO 4 D. NH 3, NH Predict whether aqueous solutions of the following compounds are acidic, basic, or neutral. Which answer is incorrect? A. KNO 3 (neutral) B. NaC 2 H 3 O 2 (basic) C. KClO (acidic) D. NaCN (basic) 23. Calculate the ph of a buffer solution which is 0.20 M in formic acid and 0.15 M in sodium formate. (K a for formic acid = 1.8 X 10 4 ) A. 2.4 X 10 4 B C D If X is the molar solubility of a slightly soluble ionic compound, which one of the following K sp expressions is incorrect? A. Ag 2 S, K sp = X 2 B. AgCl, K sp = X 2 C. BaSO 4, K sp = X 2 D. Cu(OH) 2, K sp = 4X 3

4 25. For each of the following reactions, predict whether the entropy change, S, is positive or negative: (I) 2 K (s) + Br 2 (l) 2 KBr (s) (II) 2 MnO 2 (s) 2 MnO (s) + O 2 (g) A. (I) positive, (II) positive B. (I) negative, (II) positive C. (I) positive, (II) negative D. (I) negative, (II) negative 26. Using the given values of S, calculate the value of S for the reaction C 2 H 4 (g) + H 2 (g) C 2 H 6 (g) S (J/mole K): A J/K B J/K C J/K D J/ K 27. Given the following unbalanced redox reaction: Fe 2+ + Cr 2 O 7 2 Fe 3+ + Cr 3+ What is the coefficient of Fe 3+ in the balanced equation in acidic solution? A. 1 B. 2 C. 3 D. none of these 28. Given the standard reduction potentials for the following half reactions: Cr e Cr (s) E 0 = 0.73 V Br 2 + 2e 2 Br E 0 = V What is the cell voltage, E 0 cell, for a voltaic cell using these reactions? A V B V C V D V 29. Which of the following represents a positron? A. 1 1 H B. 0 1 e C e D. 4 2 He 30. Which of the following balanced equation is labeled incorrectly? A. Beta decay, U Np e B. Alpha bombardment, 24 11Na He 13Al n C. Electron capture, 7 4 Be e 7 3 Li D. All are correctly labeled.

5 31. Which of the following pairs is incorrect? A. ethane - C 2 H 6 B. hexane - C 6 H 14 C. decane - C 10 H 22 D. heptane - C 7 H Which of the following is a general formula for a non-cyclic alkene which contains n carbon atoms and one double bond? A. C n H n B. C n H 2n+2 C. C n H 2n D. C n H 2n Classify the following molecule according to its functional group: O CH 3 CH 2 C OCH 3 A. ester B. aldehyde C. ketone D. carboxylic acid 34. What is the correct IUPAC name of the following compound? H 3 C CH 2 CH 3 C=C H 3 C Cl A. 3-chloro-2-methyl-2-pentene B. 3-chloro-4-methylpentene C. 1,1-dimethyl-1-butene D. 1-chloro-1-ethyl-2,2-dimethylpropene 35. Which of the following is the correct condensed molecular formula for isopropyl alcohol? A. CH 3 CH 2 CH 2 OH B. CH 3 CHCH 3 OH CH 3 C. CH 3 - C -CH 2 OH D. CH 3 CH 2 = CH-OH CH 3

6 PART II - Show work (5 points each) Please write your complete work in the space provided. Partial credit will be given. 1. A solution is prepared by dissolving 6.00 g of an unknown nonelectrolyte in enough water to make 1.00 L of solution. The osmotic pressure of this solution is atm at 25.0 C. What is the molecular weight of the unknown solute? 2. Rate data were obtained for the following reaction: A (g) + 2 B (g) C (g) + D (g) Experiment Initial [A], M Initial [B], M Initial Rate, M s What is a) the rate law, and b) the value of the rate constant k (with units) for the reaction?

7 3. A rainwater sample is found to have a ph of What are a) the molar concentrations of H + (aq) and OH (aq), and b) the poh of the sample? 4. A 50.0 ml sample of 0.50 M acetic acid, HC 2 H 3 O 2, is titrated with M NaOH. Calculate the ph of the solution after 25.0 ml of the base have been added. (K a for acetic acid = 1.8 X 10 5 )

8 5. If a constant current of 5.00 amperes is passed through a solution containing Cr 3+ for 1.50 hr, how many grams of Cr metal will plate out on to the cathode? 6. The half-life of strontium-90 is 28.1 years. How long will it take a 10.0 g sample of strontium-90 to decay until only 0.10 g of strontium-90 remains in the sample?

9 Answers Part I - Multiple-Choice 1. D 11. A 21. D 31. D 2. A 12. B 22. C 32. C 3. D 13. D 23. B 33. A 4. A 14. B 24. A 34. A 5. B 15. A 25. B 35. B 6. D 16. D 26. A 7. A 17. B 27. D (Ans. = 6) 8. D 18. C 28. A 9. D 19. C 29. C 10. B 20. C 30. D Part II - Show-Work 1. 1) = MRT, M = = atm = mol/l RT ( L atm / mol K)( K) 2) M = moles, moles = M X L = ( mol/l)(1.00 L) = mol L 3) moles = grams, MW = grams = 6.00 g = 196 g/mol (3 significant figures) MW moles mol 2. Rate = k[a] 2 [B] k = 200 M -2 s a) [H + ] = 10 ph = = 5.01 X 10 7 M [OH ] = 1.0 X = 2.00 X 10 8 M 5.01 X 10 7 M b) poh = -log[oh - ] = -log(2.00 X 10-8 M) = 7.70 Or, poh = 14 - ph = = 7.70

10 4. HC 2 H 3 O 2 (aq) + NaOH (aq) NaC 2 H 3 O 2 (aq) + H 2 O (l) Initially: mol mol 0 - After rxn: mol mol - ph = log(1.8 X 10 5 ) + log( mol / mol) = Coulombs = 5.00 C X 1.50 hr X 60 min X 60 s = C s 1 hr min Grams of Cr = C X 1 mol e - X 1 mol Cr X g Cr = 4.85 g C 3 mol e - mol Cr 6. k = ln(2) = ln(2) = yr 1 t 1/ yr ln(0.10 g) = ( yr -1 ) t + ln(10.0 g), t = 187 yr

Houston Community College System Departmental SAMPLE Final Exam Chemistry 1412A

Houston Community College System Departmental SAMPLE Final Exam Chemistry 1412A 1 Final Sample Exam 1412A PART I (2 points each) Multiple choice - Please DO NOT write or mark on this paper. Write your